Method of Recovery of Organic Solvents Required in Refining of Coal

ABSTRACT

A method of recovery of organic solvents required in the refining of coal comprising: mixing solvent, co-solvent and coal to form a slurry; thermally treating the slurry under pressure and high temperature to form a coal-extract; passing the coal-extract through a membrane under high pressure in an ultra filtration unit to achieve recovery of a major part of the solvent; contacting the remaining thick clarified liquid from the membrane with water to obtain precipitated coal in a slurry with a mixture of water and organic solvent; feeding the slurry to a filter to get clean coal of very low ash content as a residue and a mixture of water and organic solvent as a filtrate; distilling the filtrate to separate the balance of the organic solvent from the water. The application of a membrane for filtration minimizes the heat requirement to establish economy.

FIELD OF THE INVENTION

The invention is related to refining of coal of by organic solvents in general, and to a process of separation of coal from organic solvent completely for recovering the said solvent, which is used for extraction.

BACKGROUND OF THE INVENTION & PRIOR ART

The current process operation involves separation of coal from the organic solvents. Organic-refining or, solvent-refining or, solvent extraction of coal is a well-established technology. Abundant literature is available on the subject. However, the primary objective in most of those cases is to provide a process to produce ultra clean coal or super clean coal with ash contains less that 4%. The ash content of this parent coal (Run of Mine) is 25%. Exploratory study revealed that it is possible to extract 50% of parent coal through this process of extraction of coal under reflux conditions at atmospheric pressure. The coal contains almost 4% ash.

The yield and the ash content of super clean coal are satisfactory and it encourages for up scaling the process to bench scale set up the main concerning factor apart from yield is the economic viability of the process. The process consumes significant amount of heat for extraction. Again recovery of the of the solvent has been achieved by the consumption of large amount of heat. Combination of the above two heat inputs drives the process towards infeasibility. Now if the two heat consumptions are arranged in priority basis then heat consumption for extraction has come forth as the extraction process is solely depends upon the extraction temperature this is why it is often called as thermal extraction. So only the heat requirement for solvent recover has left for minimization. Effective or optimize design of solvent recovery such a way it minimize the heat requirement for solvent recovery and thus established the process economy.

OBJECTS OF THE INVENTION

To overcome the drawbacks of the prior art, the following innovative remedial measures were undertaken:—

Primary object of invention is to propose a method of recover of organic solvents required (for the extraction) in refining of coal.

Another object of invention is to propose an innovative approach to separate coal from organic solvent as completely as possible with minimizing energy required.

Still another object of the invention is to introduce a techno economic chemical coal benefication process without using any evaporation unit for producing clean coal and to increase recovery of solvents.

SUMMARY OF THE INVENTION

According to the innovative design, coal is separated from “coal extract” by ultra filtration. The “coal extract” is formed by the thermal treatment of coal with organic solvent. The hot coal “coal extract” is then cooled and passed through the membrane having diameter 0.2 micron or may be less than that. The filtrate coming from membrane is free from coal which is proved by the addition of water. If the permeate contains coal then addition of water, coal happens to be precipitated which does not happen at all. This observation strongly claims the inexistence of coal in permeates. It proves that the “coal extract” can be well separated by membrane operation and it produces pure solvent as permeate from membrane and the thick clarified solution from top of the membrane, which is then sent to the other unit for usual operation. The new process has been developed which is very flexible to produce clean coal of desired ash level (0.1 to 10%) with satisfactory yield.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

FIG. 1-Schematically show operation of the process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with help of the accompanying drawing which depict on exemplary embodiments of the invention. However, there can be several other embodiments, all of which are deemed covered by this description.

I) Feed Preparation Zone 1.

-   -   Coal, solvent and co-solvent are mixed thoroughly in coal in         feed preparation zone. The ratio of coal to solvent ratio is         maintained 1:18 in the feed preparation zone.

II) Extraction Zone 2

-   -   Coal slurry is then pumped to the reactor. In reactor a         temperature around 200° C. to 250° C. is maintained by         circulating hot thermic fluid. The high pressure is maintained         by inducing high pressure about 2 to 4 atm. inside the reactor.         High pressure elevates the boiling point of the solvent.         Residence time in the reactor may vary form 1 h to 1.5 h and         i.e. dictated by the techno economics of the process and its         specific requirement for a given coal. Extracted coal-solvent         mixture is then fed to a high temperature filter. From filter,         the residue is taken off and sent to the product and residue         washing zone and the filtrate is sent to the solvent recovery         zone.

III) Solvent Recovery Zone 3

-   -   The filtrate containing coal extracts which is then fed to the         membrane unit for ultra filtration. In membrane unit with the         aid of a high pressure pump filtration is done and the permeates         are collected from the membrane is free from coal which is         proved by observing no further precipitation with the addition         of water in permeate. So by incorporation of membrane 80% of         solvent is further collected without applying any heat. The         thick clarified liquid from membrane is then fed to the         precipitating tank where coal is getting precipitated as water         acts as an anti solvent.

The amount of water needed in precipitation tank is very less as 80% of solvent is already removed. This slurry (water+solvent+coal) becomes filtered by another rotary drum filter and the super clean coal is then sent to product washing unit. The filtrate contains water and organic mixture which is fed to the distillation unit and water and 19% organic solvent is being separated. So this methodology gives us almost 99% solvent recovery with negligible energy consumption, thus established the process economy.

IV) Final Product and Residue Washing Zone 4

-   -   The final operation unit is the product and residue washing         unit. The super clean coal is collected from solvent recovery         zone is washed here thoroughly and stored. Residue collected         from the extraction zone is washed properly for removing trace         amount of solvent and stored for letter use.

So in this way the whole process operation as claimed 99% solvent recovery with minimum the energy requirement, is accomplished with 50% super clean coal having ash percentage less than 4%.

-   -   The following, optical density results are supported the fact     -   1. NMP (n-methyle pyrollidone) OD=0     -   2. Recycle Solvent OD=0.23     -   3. COAL Extract OD=4

As the optical density of pure NMP is zero and the coal extract having 4, it proves that “coal extract” must contain very fine particles which can be separated by applying membrane.

The following results are the strong evidence of coal suspension in organic solvent. Actually the coal extract is very fine coal particle distribution in liquid organic phase. The particle size distribution has started approximately from 25 micron to nano size or may be less than that. The major portion of coal particle can be separated by passing through membrane. The coal extract has been passed through ceramic membrane having pore diameter of 0.2 micron. The permeate coming from the membrane is totally free of coal and this has been proved, as there is no further precipitation observed by adding sufficient amount of water. If coal is there in permeate then after adding water coal will be separated out as it was happened in our earlier process.

The important safety measures comprises:

-   -   a. As the solvent of use are organic and are flammable in         nature, it may catch fire in contact with oxygen at high         temperature. Therefore, there is provision for Nitrogen flashing         in the reactor and the Rotary drum filter unit.

The main advantages of the invention achieved

-   -   i. Recovery of solvent increases without using any thermal         energy which improves the techno-economics remarkably. 

1-9. (canceled)
 10. A method of recovery of organic solvents required in refining of coal, comprising the following steps: feeding solvent, co-solvent and coal into a feed preparation unit for mixing thoroughly to form a slurry; pumping the slurry to a reactor in an extraction unit wherein the slurry is thermally treated under pressure and allowed to settle therein for a total of specified residence time for the treatment to have all mineral matters settled, forming a coal-extract; passing the coal-extract of high temperature, through a membrane under high pressure in an ultra filtration unit of a solvent recovery zone to get permeates free from the coal, thereby achieving recovery of a major part of the solvent, the remainder being a thick clarified liquid; feeding the thick clarified liquid from the membrane to a precipitation tank residing in the solvent recovery zone and contacting it with water to obtain precipitated coal in a slurry with a mixture of water and organic solvent; feeding the slurry into a drum filter to get clean coal of very low ash content as a residue and a mixture of water and organic solvent as a filtrate; and sending the filtrate to a solvent recovery unit for distillation to separate the balance of the organic solvent from the water, wherein the use of the membrane in the process of achieving clean coal of very low ash content and complete separation and recovery of organic solvent from the thermally treated coal minimizes the heat requirement to establish economy.
 11. The method according to claim 10, wherein the coal is thermally treated in the range of 200° C.-250° C.
 12. The method according to claim 10, wherein the thermal treatment of coal is carried out under pressure in the range of 2-4 atm.
 13. The method according to claim 10, wherein the total specified time of residence in the reactor ranges from 1 hour to 1.5 hours as required for a given coal.
 14. The method according to claim 10, wherein said major part of the solvent recovered through the membrane in the ultra filtration unit is 75-80%.
 15. The method according to claim 14, wherein said membrane is a ceramic membrane having a pore diameter of up to 0.2 micron.
 16. The method according to claim 10, wherein said clean coal of very low ash content has an ash content which is in the range of 0.1-10%.
 17. The method according to claim 10, wherein said balance of recovery of the organic solvent is 10-20%.
 18. The method according to claim 10, wherein said complete recovery of the solvent is 97-99%. 